This invention relates generally to solenoid apparatus, and, more particularly, to methods for controllably positioning a solenoid plunger at a selected position between a fully retracted position and a fully extended position.
Solenoid apparatus of the kind having a reciprocable plunger are usually used in an ON/OFF mode. A spring biases the plunger toward its retracted position, and an electrical coil can be energized to drive the plunger against the spring bias to its extended position. One common use of a solenoid apparatus of this kind is as part of a fluid valve, where fluid flow is controlled in accordance with the plunger's position.
It is sometimes desirable to position the plunger at a selected position between its retracted and extended positions. In the past, this has frequently been achieved by pulsing the electrical coil at a selected duty cycle and at a frequency higher than the solenoid's response time. However, such systems are not believed to have operated in a fully optimized manner; the systems have not controllably pulsed the electrical coil based on real-time measurements or estimates of the plunger's actual position. Systems that have used a solenoid as a fluid valve, for example, have sometimes included a flowmeter for measuring the average fluid flow rate and adjusting the duty cycle at which the electrical coil is pulsed, accordingly. However, the resulting control is not believed to be as efficient as is possible and does not necessarily provide as uniform and stable a flow rate as is possible.
It should, therefore, be appreciated that there is a need for a method for controllably driving the plunger of a solenoid apparatus to a selected target position between its retracted and extended positions, with the control being based on an accurate, real-time estimation of the plunger's changing position. The present invention fulfills this need.